322 PRACTICAL ORGANIC CHEMISTRY' HINTS ON THE INVESTIGATION OF ORGANIC SUBSTANCES Provide yourself with a good book of reference, or chemist's pocket book which contains tables of physical constants. Homogeneity. — Determine if thesubstanceishomogeneous. A Liquid. — If it is a liquid, distil a few c.c. from a miniature distilling flask with a long side-tube, but no condenser, or with the apparatus shown in Fig. 86, in which the con- densing surface is sup- plied by an inner tube through which water per- colates.1 Use a thermometer and collect the distillate in a test-tube. Note the boil- ing-point, and observe if it fluctuates or remains constant and if any solid residue remains. A low boiling - point generally denotes a low molecular weight. A portion dis- tilling in the neighbour- hood of 100° may indicate the presence of water. It is useful to shake a known volume (5 c.c.) of the liquid with an equal volume of water and to note if the substance dissolves, or if any marked change in the volume of the liquid occurs. A convenient apparatus for this FIG. 86. This a If the side pie pparatus can also be used as reflux condenser or for collecting evolveti gas piece is furnished with a delivery tube dipping under water or mCrcury.